Back to EveryPatent.com
United States Patent | 6,088,176 |
Smith ,   et al. | July 11, 2000 |
An apparatus and method for reading an information signal from a magnetic storage medium using a magnetoresistive (MR) head, and separating a thermal signal component and, if present, a magnetic signal component from the information signal. A signal separation/restoration module eliminates distortion in the magnetic signal component of a readback signal induced by a thermal signal component of the readback signal. A finite impulse response (FIR) filter may be employed in the signal separation/restoration module to eliminate the distortion in the magnetic signal. The signal separation/restoration module may be employed to extract the thermal signal component from the readback signal. In one configuration, an MR head is coupled to an arm electronics (AE) module, having a highpass filtering behavior, and a signal separation/restoration module that includes an inverse filter having a transfer function inverse to that of the effective highpass filter of the AE module. The inverse filter may be an infinite impulse response (IIR) filter. In another embodiment, the magnetic and thermal signal components of a readback signal are respectively extracted and processed so as to linearly correspond to head-to-disk spacing. Head-to-disk spacing change using the thermal signal is used to detect disk surface defects, topographic variations, and servo control surface variations.
Inventors: | Smith; Gordon J. (Rochester, MN); Ottesen; Hal Hjalmar (Rochester, MN); Abraham; David William (Ossining, NY); Praino; Anthony Paul (Poughquag, NY); Re; Mark Edward (Los Gatos, CA); Wickramasinghe; Hemantha Kumar (Chappaqua, NY) |
Assignee: | International Business Machines Corporation (Armonk, NY) |
Appl. No.: | 581877 |
Filed: | January 2, 1996 |
Current U.S. Class: | 360/46; 360/25; 360/31; 360/75 |
Intern'l Class: | G11B 005/09 |
Field of Search: | 360/113,77.06,77.01,103,67,75,137,46,48,32,66,77.05,77.04,59,25,31 324/210,212,252,207.21,235 374/4,6,9 164/141,45 369/58,116,275.1 388/812 395/442 73/866.4,104 361/111 327/311 364/724.16 |
3416373 | Dec., 1968 | Havens. | |
3918091 | Nov., 1975 | Walraven et al. | 360/77. |
4430010 | Feb., 1984 | Zrenner et al. | 374/45. |
4485337 | Nov., 1984 | Sandusky | 388/812. |
4498146 | Feb., 1985 | Martinez | 395/442. |
4532802 | Aug., 1985 | Yeack-Scranton et al. | 73/866. |
4647992 | Mar., 1987 | Vinal | 360/77. |
4669011 | May., 1987 | Lemke | 360/103. |
4691259 | Sep., 1987 | Imakoshi et al. | 360/113. |
4712144 | Dec., 1987 | Klaassen | 360/67. |
4747698 | May., 1988 | Wickramsinghe et al. | 374/6. |
4762427 | Aug., 1988 | Hori et al. | 374/141. |
4777544 | Oct., 1988 | Brown et al. | 360/75. |
4802033 | Jan., 1989 | Chi | 360/77. |
4853810 | Aug., 1989 | Pohl et al. | 360/103. |
4914398 | Apr., 1990 | Jove et al. | 361/111. |
4931887 | Jun., 1990 | Hegde et al. | 360/75. |
4949036 | Aug., 1990 | Bezinque et al. | 324/212. |
5032935 | Jul., 1991 | Jove et al. | 360/67. |
5054936 | Oct., 1991 | Fraden | 374/164. |
5057785 | Oct., 1991 | Chung et al. | 327/311. |
5070495 | Dec., 1991 | Bletscher, Jr. et al. | 369/116. |
5079663 | Jan., 1992 | Ju et al. | 360/113. |
5084791 | Jan., 1992 | Thanos et al. | 360/77. |
5130866 | Jul., 1992 | Klaassen et al. | 360/75. |
5168413 | Dec., 1992 | Coker et al. | 360/137. |
5185681 | Feb., 1993 | Volz et al. | 360/77. |
5212677 | May., 1993 | Shimote et al. | 369/58. |
5233482 | Aug., 1993 | Galbraith et al. | 360/46. |
5258940 | Nov., 1993 | Coker et al. | 364/724. |
5301080 | Apr., 1994 | Ottesen et al. | 360/113. |
5321559 | Jun., 1994 | Nguyen et al. | 360/46. |
5327298 | Jul., 1994 | Ottesen et al. | 360/48. |
5345342 | Sep., 1994 | Abbott et al. | 360/48. |
5367409 | Nov., 1994 | Ottesen et al. | 360/32. |
5377058 | Dec., 1994 | Good et al. | 360/75. |
5388014 | Feb., 1995 | Brug et al. | 360/66. |
5402278 | Mar., 1995 | Morita | 360/77. |
5418770 | May., 1995 | Ide et al. | 369/116. |
5424885 | Jun., 1995 | McKenzie et al. | 360/77. |
5430706 | Jul., 1995 | Utsunomiya et al. | 369/275. |
5455730 | Oct., 1995 | Dovek et al. | 360/113. |
5739972 | Apr., 1998 | Smith et al. | 360/77. |
5751510 | May., 1998 | Smith et al. | 360/77. |
Foreign Patent Documents | |||
0 242 597 | Oct., 1987 | EP. | |
61-177622 | Aug., 1986 | JP. | |
63-191316 | Aug., 1988 | JP. | |
1-98180 | Apr., 1989 | JP. | |
4-95218 | Mar., 1992 | JP. | |
4-109421 | Apr., 1992 | JP. | |
4-141822 | May., 1992 | JP. | |
5-174515 | Jul., 1993 | JP. | |
06290563 | Oct., 1994 | JP. |
S. Z. Dushkes and R. J. Surty, "Head Crash Detector", May 1971, IBM Technical Disclosure Bulletin, vol. 13, No. 12, p. 3685. L. R. Bellamy and J. D. Luciani, "Disk Drive Motor Speed Control", Apr. 1981, IBM Technical Disclosure Bulletin, vol. 23, No. 11, p. 5163. E. G. Gruss and A. R. Tietze, "Servo System for Magnetic Recording Based on Time Comparison", Jul. 1980, IBM Technical Disclosure Bulletin vol. 23, No. 2, pp. 787-789. R. E. Fontana, Jr., D. E. Horne and H. Sussner, "Disk Asperity Detector", Aug. 1983, IBM Technical Disclosure Bulletin, vol. 26, No. 3A, pp. 1278-1280. G. J. Kerwin, J. M. Poss and D. P. Swart, "Fast Offset Recovery for Thermal Asperity Data Recovery Procedure", Apr. 1992, IBM Technical Disclosure Bulletin, vol. 34, No. 11, pp. 217-219. K. B. Klaassen, "Magnetic Recording Channel Front-Ends", Nov. 1, 1991, IBM Research Report, pp. 1-6. Research Disclosure, "Asperity Knee Detection Using Harmonic Ratio Flyheight", Mar. 1991, Emsworth Design, Inc., No. 323, p. 190. Chau Lin, "Techniques for the Measurement of Air-Bearing Separation-A Review", Dec. 1973, IEEE Transactions on Magnetics, vol. MAG-9, No. 4, pp. 673-677. F. W. Gorter et al., "Magnetoresistive Reading of Information", Sep. 1974, IEEE Transactions on Magentics, vol. MAG-10, No. 3, pp. 899-902. F. E. Talke et al., "Surface Defect Studies of Flexible Media Using Magnetoresistive Sensors", Sep. 1975, IEEE Transactions on Magnetics, vol. MAG-11, No. 5, pp. 1188-1190. Shoji Tanaka, et al., "Characterization of Magentizing Process for Pre-Embossed Servo Pattern of Plastic Hard Disks", Mar. 1994, IEEE Transactions on Magnetics, vol. 30, No. 2, pp. 4210-4211. Hiroaki Yada et al., "High Areal Density Recording Using an MR/Inductive Head and Pre-Embossed Rigid Magnetic Disk", Mar. 1994, IEEE Transactions on Magentics, vol. 30, No. 2, pp. 404-409. Y. Li et al., "The Determination of Flash Temperature in Intermittent Magentic Head/Disk Contacts Using Magnetoresistive Heads", Jan. 1993, Journal of Tribology, vol. 115, No. 1, pp. 179-184. Shoji Tanaka et al., "Characterization of Magnetizing Process for Pre-Embossed Servo Pattern of Plastic Hard Disks", Nov. 1994, IEEE Transactions on Magnetics, vol. 30, No. 6, pp. 4209-4211. Kenjiro Watanabe et al., "Demonstration of Track Following Technique Based on Discrete Track Media", Nov. 1993, IEEE Transactions on Magnetics, vol. 29, No. 6, pp. 4030-4032. K. Watanabe et al., Demonstration of Track following Technic Based on Discrete Track Media, pp. 1-3. Osamu Morita et al., "Magnetizatin Characteristics of Pre-Embossed Patterns on the Molded Plastic Rigid Disk." |
TABLE 1 ______________________________________ Peak Response to Surface Defects and Servo Sectors Thermal Spacing Magnetic Spacing Type of Defect Signal Signal ______________________________________ Pit Positive Positive Bump Negative Positive Thermal Asperity Large Positive Negative Magnetic Void None Positive Servo Sector None Negative and Positive ______________________________________
TABLE 2 ______________________________________ Comparator Logic Levels TA BUMP PIT Pass/Fail Criteria ______________________________________ 0 0 0 Pass 0 0 1 Pass 0 1 0 Fail (bump) 0 1 1 Fail (gouge) 1 0 0 Fail (TA) 1 0 1 Fail (TA) 1 1 0 Fail (large bump) 1 1 1 Fail (bump with TA) ______________________________________